1. The Field of the Invention
The invention relates to a vacuum heat treating furnace for the heat treatment of metal workpieces. Specifically the invention relates to a furnace wherein uniform heating and cooling is achieved in a simple manner.
2. Description of the Prior Art
In vacuum furnaces of the type of the present invention, which are preferably used for vacuum hardening, it is important that all surfaces of the workpieces to be treated are cooled in the cooling phase as evenly as possible. This results in the entire structure formed by the treatment having a uniformly good quality and that the workpiece will not be deformed by thermal stresses.
In vacuum furnaces of the above type, which are known and disclosed in published German patent disclosure DE-OS 32 15 509, attempts have been made to obtain uniform workpiece cooling by alternately passing or guiding cooling gases from nozzles arranged in the ceiling of the heating chamber into two gas outlet slots arranged laterally at the bottom of the heating chamber. In addition, cooling gases are blown from nozzles arranged in the bottom of the heating chamber, into two gas outlet slots arranged laterally at the ceiling of the heating chamber. By frequently reversing the stream of gas acting on the workpieces it is possible to achieve a more even cooling of the workpieces, as compared to having the cooling gas flowing in only one direction during the treatment process. However, it is impossible to cool the top side of the workpieces at the same rate as the cooling of the bottom side of the workpieces. This results in differences in the structure and thermal stresses between the workpiece top and bottom.